N-Alkyl Interstitial Spacers and Terminal Pendants Influence the Alkaline Stability of Tetraalkylammonium Cations for Anion Exchange Membrane Fuel Cells

Sean A. Nuñez, Clara Capparelli, Michael A. Hickner

Research output: Contribution to journalArticle

76 Scopus citations

Abstract

Current performance targets for anion exchange membrane (AEM) fuel cells call for greater than 95% alkaline stability for 5000 h at temperatures of up to 120 °C. Using this target temperature of 120 °C, we provide an incisive 1H nuclear magnetic resonance-based alkaline degradation method to identify the degradation products of n-alkyl spacer tetraalkylammonium cations in various AEM polymers and small molecule analogues. The operative alkaline degradation mechanisms and rates on benzyltrimethylammonium-, n-alkyl interstitial spacer-, and n-alkyl terminal chain-cations are compared in several architectures. Our findings indicate that benzyltrimethylammonium and n-alkyl terminal pendant cations are significantly more labile than an n-alkyl interstitial spacer cation. Additionally, we found that the alkaline stability of an n-alkyl interstitial spacer cation is enhanced when it is combined with an n-alkyl terminal pendant. At 120 °C, an inverse trend was observed in the overall stability of AEM poly(styrene) and AEM poly(phenylene oxide) samples compared to what has been shown at 80 °C. Follow-up small molecule studies suggest that at 120 °C, a 1,4-elimination degradation mechanism may be activated on styrenic AEM polymers capable of forming hyperconjugated resonance hybrids.

Original languageEnglish (US)
Pages (from-to)2589-2598
Number of pages10
JournalChemistry of Materials
Volume28
Issue number8
DOIs
StatePublished - May 10 2016

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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